Firstly, thanks for reply.
My add-on have drag & drop feature, but if there isn't this code, Firefox says on console: "Content Security Policy: The page's settings blocked the loading of a resource at ..." and the feature isn't working. When I researched, I saw this solution on StackoverFlow.
The add-on is just about bookmarks and new tab.
Actually, I changed my browser about:config too. I hope, this add-on works without about:config settings.
If, there is a problem, please help me and give me an advice.